1. Field of the Invention
The present invention relates to resin compositions being excellent in gas barrier properties and improved in flexibility, represented by resistance to falling shock, flexural resistance, air-back prevention, skin-pack adaptability, shrink-film packagability and in transparency, and also to multilayered structures comprising at least one layer of said composition.
2. Description of the Prior Art
Saponified product of ethylene-vinyl acetate copolymer (hereinafter referred to as EVOH) is a thermoplastic resin excellent in gas barrier properties, resistance to oil and odor keeping property as compared with other resins and is used for gas-barrier layer for various gas-barrier films and gas-barrier containers. However, multilayered films and multilayered containers comprising EVOH as gas-barrier layer often encounter problems resulting from high rigidity of the EVOH. For example, multilayered films and containers filled with contents often break or destroy when dropped onto the ground, pinholes readily generate on multilayered films filled with contents due to bending or vibration during transportation, air-back tends to generate on multilayered tubes, creases generate upon skin-packing, insufficient stretchability and shrinkage of shrink-packing films, and so forth.
Blending EVOH with other thermoplastic resins or plasticizers to improve these drawbacks has been proposed. For example, there are currently employed a process which comprises blending EVOH with a plasticizer such as butylene glycol or dioctyl phthalate and a process which comprises blending EVOH with an ethylene-vinyl acetate copolymer, ethylene-vinyl carboxylate copolymer, ethylene-acrylic acid ester copolymer, ethylene-vinyl carboxylate copolymer modified with an .alpha.,.beta.-unsaturated carboxylic acid or its anhydride or the like. However, the blending of plasticizers has drawbacks of bleeding of the plasticizers and low mechanical properties of the resulting molded articles, and the blending of the above copolymers impairs, while exhibiting a large effect of increasing flexibility and resistance to shock, the transparency that is a specific feature of EVOH.
Compositions comprising EVOH and polyamide are known to have high transparency, but they have other drawbacks of decreased gas barrier properties and poor thermal stability at molding, thereby forming gels in a short time. The compositions therefore have not been used in practice.
Japanese Patent Publication No. 48512/1976 and Japanese Patent Application Laid-open No. 161447/1985 disclose blending EVOH with a partially saponified product of ethylene-vinyl acetate copolymer (hereinafter referred to as "partially saponified EVA) and that the use of this blend provides interlayer adhesiveness between EVOH and polyolefin and low-temperature heatsealability. However, when molded articles such as film are prepared according to the procedure given in the prior art, there occur problems of low flexibility, poor thermal stability, poor moldability with vigorous neck-in and the like, and further the obtained articles show streaks and pear-skin patterns on the surface, and the process has not yet been put into practice.
The Japanese Patent Publication No. 48512/1976 also describes blending EVOH with a partially saponified EVA and further incorporating into the resultant composition an polyolefin (e.g. ethylene-vinyl acetate copolymer) in an amount of not more than 60% by weight based on the total weight of the partially saponified EVH and the polyolefin. However, the incorporation of polyolefin in an amount of 60% by weight leads to formation of streaks and pear-skin patterns on the surface of the molded film, which is not preferred. This fact is clear from Comparative Example 5 later described herein.
Japanese Patent Application Laid-open Nos. 11050/1982 and 32952/1982 disclose blending EVOH with a partially saponified EVA and blending the resultant composition with an ethylene-vinyl acetate copolymer in an weight ratio of not more than that of the partially saponified EVA, to obtain a multilayered container having excellent adhesiveness between polyolefin layer or polyvinyl chloride layer. However, the incorporation of an ethylene-vinyl acetate copolymer in an weight ratio of not more than that of a partially saponified EVA contained creates streaks and pear-skin pattern on the film surface, which is not preferred. This fact is also clear from Comparative Example 5 later described herein.
EP-A 326827 discloses blending EVOH with a partially saponified EVA, but it does not describe about further incorporation of an ethylene-vinyl acetate copolymer.
Japanese Patent Application Laid-open No. 39380/1978 discloses blending 100 parts by weight of a polyolefin (e.g. ethylene-vinyl acetate copolymer) with 5 to 40 parts by weight of a partially saponified EVA, to obtain a laminate having excellent adhesiveness between the composition layer and a polyolefin layer. However, this large amount of polyolefin incorporated will not give a laminate having excellent gas barrier property. This is clear from Comparative Example 7 later described herein.
Japanese Patent Application Laid-open No. 74354/1983 discloses lamination of a laminate of a polyethylene (PE) layer with a layer of a blend comprising 10 to 100 wt % of EVOH, 0 to 85 wt % of EVA and 0 to 90 wt % of partially saponified EVA, the PE layer of which has been treated with ozone, with an anchor-treated base layer; and, in the Example, the use of a blend comprising 31 wt % of EVOH, 65 wt % of EVA and 9 wt % of partially saponified EVH. However, this application only describes the blend of the above composition as being best for transparency, and does not describe the teaching that blending of the above three components in specific amounts can minimize generation of streaks and pear-skin patterns of the resulting molded articles. Besides, with the blend having the composition described in the Example of this application, the molded articles will have pear-skin patterns on the surface thereof and poor gas barrier properties, as shown in the Comparative Example 6 which is described later herein.
As stated heretofore, there has not been obtained a resin composition or multilayered structure comprising EVOH and having well-balanced properties of resistance to falling shock, flexural resistance, prevention of air-back, skin-pack adaptability, shrink-pack capability and the like.